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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

ALLEN GLACIER AND OTHER ICE TONGUES                 449
the type formed by a minor advance of a glacier across the unconsolidated deposits of a previous retreat. These parallel ridges were crossed at various angles by narrow deposits of sand and clay. Some of the latter were 8 or 4 feet high (PI. CLXXni, A) and rather sinuous. Those at the glacier margin had cores of ice.
The marginal lake at the eastern end of the glacier is the first one seen from the train going northward. Its ice wall is completely covered with growing forest and slopes at a moderate angle.
The northern marginal lake, the largest bordering Heney Glacier and also well seen from the railway, is about a mile long and half to three quarters of a mile wide. It has the terminal moraine on the north and east sides, outwash gravels on the west, and the glacier on the south. This glacier margin, which is in the zone of barren ablation moraine, has been undercut by the lake waters, so that it forms a precipitous cliff, 20 to 50 feet high. At the tune of our studies ice blocks were occasionally sliding down into the water, more at night than during the day. The lake is probably very shallow, for no icebergs were afloat upon it.
The Outwash Gravels. The deposits made by the glacial streams from Heney Glacier merge with those of the Copper River. The largest alluvial fan is on the south and is barren near the present streams and thickly covered with alder elsewhere. The modern outwash gravels west of the largest lake are barren and surround remnants of older outwash which is forested.
Vegetation on Heney Glacier. The trees and moss on the portion of the glacier which is covered with ablation moraine and upon the terminal moraine furnish some facts regarding the recent history of the terminal bulb. The absence of annual plants and of moss on the western belt of ablation moraine show that melting of the ice has resulted in slumping for some time in the past. The presence of moss and of a dense growth of mature trees on the eastern extremity shows that it has long been immune from slumping, and yet, even here, the rare areas of dead and overturned trees show that the ice lies at no great distance below the surface. Upon the outer margin of the glacier and upon the terminal moraine near Mile Post 75 the alders and cottonwoods were 11 to 26 inches in diameter and 50 to 76 years old in 1910, but at the extreme northwestern edge of the terminal moraine, near Mile Post 77 there were cottonwoods over 90 years old. This shows clearly that the last expansion of the bulb of Heney Glacier was about a century ago and that for over 76 years there has been no period of activity capable of breaking up the outer portion of the bulb.
Near the outlet of the large northern lake the crest of a high knob in the terminal moraine showed great cracks in 1910. As the rocks were thickly covered with moss and the ridge was forested this raised the question as to whether the ice still underlies this moraine and the lake basin. We saw nothing elsewhere that led us to suspect ice beneath this moraine, the remainder of which is forested and undisturbed by slumping.
Activity of Heney Glacier in 1911. It has been stated that the glacier was only moderately crevassed in 1910. The crevasses in the valley tongue seemed to be of two sorts, one set were the normal crevasses of the more rapidly moving upper glacier reduced by ablation, the other a longitudinal series of fresh-looking gashes which had sliced the glacier into long flat-topped seracs. This latter series extended into the edge of the zone of barren ablation moraine, where none of the older crevasses were left. That
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